Image-guided surgery is a developing technology that allows surgeons to perform an intervention or a surgery in a minimally invasive way while being guided by images, which may be “real” images or virtual images. For instance, in laparoscopic surgery, a small video camera is inserted through a small incision made in the patient skin. This video camera provides the operator with a “real” image of the anatomy. In other types of image-guided surgery, such as endo-vascular surgery where a lesion is treated with devices inserted through a catheter navigated into the arteries of the patient, are “image-guided” because low dose x-ray images (also called fluoroscopy images) are used to guide the catheters and the devices through the patient anatomy. The fluoroscopy image is a “real” image, not a virtual image, as it is obtained using real X-rays and shows the real anatomy of the patient. Then there are also cases where a “virtual” image” is used, which is a combination of real images utilized to form the virtual image of the anatomy in a known manner. An example of image-guided surgery using both “real” and “virtual” images is the minimally invasive surgery of spine, where “real” fluoroscopy images acquired during the surgery are used to guide the insertion of devices in the vertebras, while pre-operative CT or Cone-beam CT (CBCT) images are also used, in conjunction with surgical navigation systems, to visualize the location of the devices in the 3D anatomy of the patient. Because the display of the location of the devices in the CT or CBCT images does not result of a direct image acquisition performed during the surgery, as there is not a CT in the operating room, but from a combination of pre-existing real images and information provided by the surgical navigation system, the display of the device location in the CT or CBCT images is described as a “virtual” image.
Regardless of particular images utilized in its formation, image-guided surgery allows the surgeon to reduce the size of entry or incision into the patient, which can minimize pain and trauma to the patient and result in shorter hospital stays. Examples of image-guided procedures include laparoscopic surgery, thoracoscopic surgery, endoscopic surgery, etc. Types of medical imaging systems, for example, radiologic imaging systems, computerized tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), ultrasound (US), X-ray angiography machines, etc., can be useful in providing static image guiding assistance to medical procedures. The above-described imaging systems can provide two-dimensional or three-dimensional images that can be displayed to provide a surgeon or clinician with an illustrative map to guide a tool (e.g., a catheter) through an area of interest of a patient's body.
In clinical practice, minimally invasive percutaneous cardiac and vascular interventions are becoming more prevalent as compared with traditional open surgical procedures. Such minimally invasive percutaneous cardiac and vascular interventions have advantages of shorter patient recovery times, as well as faster and less risky procedures. In such minimally invasive cardiac and vascular interventions, devices such as stents or stent grafts are delivered into the patient through vessels via a catheter. Navigating the catheter inside the vessels of a patient is challenging. To assist in the navigation, X-ray fluoroscopy is typically used to visualize the catheter during the procedure. However, this imaging modality does not capture soft tissue structure of the patient well.
In particular, during one exemplary type of cardiac and vascular interventional procedure, i.e., an endo-vascular aneurysm repair (EVAR) procedure, the operator inserts and deploys an endograft in the aorta under fluoroscopy guidance. To achieve this task, the operator needs obviously to see the devices, which is easily achieved using fluoroscopy, but he/she also needs to understand the location of the devices versus the vascular anatomy, which is more challenging.
Since the arteries are not spontaneously visible under fluoroscopy, X-ray sequences taken after injection of a contrast agent have to be acquired to visualize the arteries. However the use of the contrast agent has a number of significant drawbacks. First, the contrast agent requires a significant time to become effective and has a limited time for effectiveness within the patient before additional contrast medium is require. Second, the contrast agent can have certain adverse effects on the patient in larger amounts, such as required for multiple X-ray sequences, including the contribution to the potential development of patient nephropathy as a result of the amount of contrast agent being injected. Third, the increased number of X-ray sequences necessarily increases the total X-ray exposure to both patient and staff as a result of the multiple X-ray sequences being taken.
More recently, solutions based on the fusion of a pre-operative 3D computed tomography angiography (CTA) image that shows the anatomy of the patient through which the interventional tool is to be navigated with the fluoroscopy images have been recently proposed to improve the EVAR guidance. In this process, as shown in FIG. 1, a pre-op CTA image 1000 is obtained and subsequently registered or fused with an intra-operative fluoro or X-ray image 1002, such as by overlaying the fluoro image onto the CTA image or vice versa, to illustrate a fusion image 1004 illustrating both the structure of the anatomy of the patient and the current location of the interventional tool, e.g., a guide wire or catheter, within the anatomy. These fusion image solutions can more clearly illustrate the interventional tool location within the patient anatomy, and have been shown to contribute to the reduction of both the volume of injected contrast agent and the X-ray exposure to the patient.
However, one significant drawback of the fusion image solution for interventional procedures, such as an EVAR procedure, is that the insertion of the interventional devices themselves during the interventional procedure deforms the anatomy of the aorta, and in particular straightens the aorta thereby moving the location of the ostia of visceral arteries from the anatomy illustrated in the pre-op CTA images. As a consequence, after insertion of the interventional device, the anatomy depicted by the pre-op CTA image no longer matches the current patient anatomy and cannot provide an accurate roadmap for the navigation of the device through the anatomy.
To solve this anatomy deformation issue, the operator has to acquire an x-ray based 2D digital subtraction angiography (DSA) series after insertion of the device(s) and use this DSA series to manually correct for the deformation of the aorta. This solution for deformation correction is sub-optimal for two reasons. First, it utilizes an injection of contrast agent to the patient, which is directly contradictory to one of the objectives of 3D roadmap/fusion image, which is to reduce the amount of contrast agent required to be injected into the patient. Second, the final registration accuracy provided by the DSA correction may still be limited. Since the deformation of the anatomy takes place in 3D, it is not possible, from just one 2D DSA acquired in one angulation, to find a correction that would adequately reflect deformations for the ostia of all visceral arteries.
One additional solution has been the combination of CT images with ultrasound images to identify changes in the positioning of fiducial and anatomical landmarks in the images of the patient anatomy. For example, in prior art combined CT/ultrasound imaging methods, such as that disclosed in Kaspersen et. al., Three-Dimensional Ultrasound-Based Navigation Combined with Preoperative CT During Abdominal Interventions: A Feasibility Study, Cardiovase Intervent Radiol (2003) 26:347-356, separate pre-op CT images are compared with intra-op ultrasound images to compare the position of fiducial and/or anatomical landmarks in order to determine the differences between the anatomy illustrated in the CT image and in the ultrasound image by illustrating the images side-by-side or by overlaying the images with one another. These differences are then utilized by the physician to interpret the current configuration for the patient anatomy in order to perform the interventional procedure.
However, while this image combination provides the physician with the ability to interpret the differences in the displayed anatomies, it is completely left to the experience and discretion of the physician to utilize the displayed information to identify the location and extent of any deformations in the displayed patient anatomy in each if the respective CT and ultrasound images. When this is done during an interventional procedure by directly comparing the CT and ultrasound images, this requires the physician to make decision on potentially incomplete information and to do so by taking focus off of the procedure being performed, both of which are undesirable.
As a result, it is desirable to develop an imaging system and method that can improve upon existing systems and methods for the correction of anatomy deformation in interventional procedures, such as EVAR procedures.